Conventional incandescent lamps such as the common A19 bulb size typically provide a relatively uniform distribution of light. Specifically, the intensity of light measured at a fixed distance but at different angles from a centerline axis through the bulb is relatively constant. In addition to consumer appeal, this uniformity may be necessary for certain applications.
As compared to incandescent lamps, other types of light emitting devices are available that have certain advantages. For example, light emitting diodes (LEDs) can provide a light output comparable to an incandescent lamp but at a significantly improved energy efficiency. Additionally, the lifetime of an LED lamp can be substantially longer than an incandescent lamp.
The LEDs can be configured in a lamp that includes a threaded base (sometimes referred to as an “Edison base”) such that it is interchangeable with conventional incandescent lamps. A diffuser can also be provided that, in addition to light scattering, can provide an LED lamp with a shape similar to that of conventional incandescent lamps. The color and intensity of light provided by the LED can also be similar to incandescent lamps.
However, certain challenges remain for the use of non-incandescent lamps. For example, LED lamps require an associated circuit board and generate significantly more heat than an incandescent lamp of comparable light output. In addition, LEDs act close to lambertian sources and thus they alone typically do not provide a uniformly distributed omnidirectional light output. LED devices are usually flat-mounted on a circuit board such that the light output is substantially along a line perpendicular to the plane of the circuit board.
As such, the circuit board and heat management features contribute to the optical losses different along each direction causing the non-uniformity of the light distribution from the LEDs. Providing more energy to the LEDs can increase the amount of light output, but still may not provide uniformity. However, this also increases the amount of heat generated, which will degrade LED performance unless additional thermal management is undertaken such as larger cooling features. Yet, the size of the overall lamp may be limited depending upon the intended application or conventional lamp form desired.
Accordingly, an optical element or lens for more uniformly distributing the light from a source that includes one or more LEDs or alternatively chip-on-board LED having tightly packed multiple chips together would be useful. More particularly, an optical element that can provide lighting having smaller variations in light intensity but varying angles from the LEDs would be beneficial. A lighting apparatus or lamp incorporating such an optical element would also be useful.